The present invention relates to a document ejection apparatus for an automatic document conveyance apparatus, and more particularly to an automatic document conveyance apparatus wherein a document ejection speed is reduced immediately before the completion of document ejection when a document is ejected through an outlet.
In an automatic document conveyance apparatus (hereinafter referred to as ADF) of a copying machine, a document that is set on a document tray is automatically conveyed to a document table and is ejected, after an copying operation made by the copying machine, onto a document ejection tray. The apparatus is suitable for high speed copying for a number of documents in a sheet form. Especially on the recent copying machines, the document conveyance speed in ADF has also been raised (approximately, 1000-1200 mm/sec) under the influence of a copying speed increased for raising copying efficiency. When documents are ejected onto an ejection tray at such a high speed, the documents tend to be ejected irregularly onto the ejection tray, or tend to jump out to the ejection tray, which has been a problem.
For the purpose of solving the problem mentioned above, various suggestions have been made. In Japanese Patent Publication Open to Public Inspection No. 178363/1986 [hereinafter referred to as Japanese Patent 0.P.I. Publication] (conventional example 1), for example, there is disclosed a technology comprising a sheet sensor that is provided immediately before a document ejection roller and detects the transit of a document and further comprising a document ejection roller-decelerating means that reduces the speed of revolution of the document ejection roller when the sheet sensor detects the transit of a trailing edge of the document.
In the technology disclosed in Japanese Patent 0.P.I. Publication No. 12564/1987 (conventional example 2), on the other hand, there is provided a switching means capable of changing the speed of document ejection either to the first ejecting speed that is the same as a document conveyance speed or to the second ejecting speed that is lower than the first speed by switching the revolution of a document ejection means.
Further, in the technology disclosed in Japanese Patent O.P.I Publication No. 70159/1987 (conventional example 3), the ejection speed is reduced by a brake and a clutch when the trailing edge of a document to be ejected is detected by a sensor.
Furthermore, in the technology disclosed in Japanese Patent 0.P.I. Publication No. 111854/1987 (conventional example 4), a document conveyance speed is reduced for a certain period of time after the trailing edge of a document is detected.
Each of aforesaid suggested technologies has its own special features and is effective as measures. However, each of them is not perfect. In Conventional Examples 1 and 4, for example, when a conveyance belt and a document ejection roller are driven by only a single motor, the reduction in speed of the motor is that in speed of the conveyance belt, and it is difficult to convey the next document onto a platen glass while the previous document is ejected, which adversely affects the improvement of productivity of copying. When an additional motor is used, which is different from Conventional Example 1, it is not advantageous in terms of cost. Further, in Conventional Example 2, a gear train for driving is complicated and it requires many gears, resulting in the high cost.
In Conventional Example 3, on the other hand, the combination of a brake and a clutch is complicated and requires many parts, resulting in the high cost and the durability of a clutch which is doubtful.
As stated above, it is necessary to reduce the sheet ejection speed for eliminating that documents are ejected onto an ejection tray irregularly. It has been confirmed experimentally that the linear of a document with which documents are ejected regularly onto an ejection tray that is positioned almost horizontally is 400 mm/sec or less. However, when an automatic document conveyance apparatus is driven totally with the document conveyance speed of 400 mm/sec or less, the ratio of Opm (number of documents to be fed per minute in ADF) to Cpm (number of copies made per minute on a copying machine), namely, the copy productivity (p =Opm/Cpm) is reduced. When Cpm on the copying machine side is made high (e.g. 50-70 copies of A4 size per minute), it is desired to obtain the copying productivity of 100% of such copying rate by achieving a high speed conveyance of documents that is balanced with the copying rate. Further, in order to raise aforesaid linear speed more and yet to achieve the better registration of ejected documents on a sheet ejection tray, the sheet ejection tray has conventionally been inclined and documents to be ejected out of a copying machine have been compelled to climb along the inclined sheet ejection tray to reduce their speed. The total height of an ADF with such a structure tends to be greater, and when the ADF is of a type wherein the ADF swings for opening away from an operator, a part of the ADF may hit the wall behind a copying machine. In order to avoid this, additional space must be provided at the rear side of the copying machine, which results in an increase of floor space for installation.